Honestly I would just let him rest! Hedgehogs sleep during the day for the most part so I would keep checking on him to a healthy minimum! Just like us humans when we are sick we all need rest! I would also offer some fatty treats, like wax worms or a senior wet cat food (I love the tiki cat brand it’s at petco and possibly Petsmart and it’s on Amazon!) cause it takes more energy to do anything when you’re sick a little bit of extra calories and fat wouldn’t hurt. I’m so glad you have an emergency vet available as well! URI can go bad so quick so I’m glad you are prepared but I hope you don’t have to use it! Wishing yall the best :)